For the first time, a generation of children is going through adolescence with smartphones ever-present. Jean Twenge, a professor of psychology at San Diego State University, has a name for these young people born between 1995 and 2012: "iGen."

She says members of this generation are physically safer than those who came before them. They drink less, they learn to drive later and they're holding off on having sex. But psychologically, she argues, they are far more vulnerable.